Heat dissipating material and semiconductor device using same

ABSTRACT

Disclosed is a heat dissipating material which is interposed between a heat-generating electronic component and a heat dissipating body. This heat dissipating material contains (A) 100 parts by weight of a silicone gel cured by an addition reaction having a penetration of not less than 100 (according to ASTM D 1403), and (B) 500-2000 parts by weight of a heat conductive filler. Also disclosed is a semiconductor device comprising a heat-generating electronic component and a heat dissipating body, wherein the heat dissipating material is interposed between the heat-generating electronic component and the heat dissipating body.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.12/161,659, filed Jul. 21, 2008, which is based upon PCT National StageApplication No. PCT/JP2007/051132 filed Jan. 25, 2007, and claims thebenefit of priority from prior Japanese Patent Application No.2006-018017, filed Jan. 26, 2006, and the entire contents of each ofthese applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a heat dissipating material that isexcellent in thermal conductivity and not prone to oil bleeding and to asemiconductor device which has the heat dissipating material interposedbetween a heat-generating electronic component and a heat dissipatingbody.

BACKGROUND ART

Conventionally, a heat dissipating body such as a heat sink is widelyused for many of heat-generating electronic components in order toprevent damage, performance degradation and the like due to an increasein temperature during use. For efficient conduction of the heatgenerated from the heat-generating electronic component to the heatdissipating body, a heat conductive material is used between theheat-generating electronic component and the heat dissipating body.

It is known to use a heat dissipating sheet or a heat dissipating greasefor the heat conductive material. Generally, heat dissipating grease hasproperties similar to a liquid, and compared to heat dissipating sheets,can adhere tightly to the heat-generating electronic component and theheat dissipating body to decrease interfacial thermal resistance withoutbeing influenced by surface irregularities of the heat-generatingelectronic component and the heat dissipating body. However, the heatdissipating grease tends to bleed oil component when used for anextended period.

For example, Patent Reference 1 proposes a heat dissipating siliconegrease having a heat conductive filler contained in a base oil of aparticular polyorganosiloxane. Patent Reference 2 proposes a heatdissipating material which contains polyorganosiloxane having a vinylgroup bonded to a silicon atom, polyorganohydrogensiloxane having ahydrogen atom bonded to a silicon atom and a heat conductive filler, andis gelated by a cross-linking reaction in the presence of a platinumbased catalyst.

It is generally known that such a conventional heat dissipating materialhas the heat conduction performance improved by high filling of the heatconductive filler. However, since the conventional heat dissipatingmaterial tends to cause lowering of workability in the productionprocess, the upper limit of its blending amount is restricted.Therefore, due to the further increase in heat generation resulting fromrecent trends of higher densities and performance of heat-generatingelectronic components, a sufficient heat conduction effect cannot beobtained by the conventional heat dissipating material. Furthermore, oilbleeding is not reduced sufficiently, allowing free oil component tobleed from a gel-like cured material due to external pressures such asswaging or the like, and electronic parts are easily contaminated. Thecontamination tends to prevent the achievement of the originalperformance of the electronic parts or to cause them to operate poorly.

-   Patent Reference 1: JP-A 2003-301189 (KOKAI)-   Patent Reference 2: JP-A 2002-294269 (KOKAI)

DISCLOSURE OF THE INVENTION

According to an aspect of the present invention, there is provided aheat dissipating material excelling in thermal conductivity and notprone to oil bleeding and a semiconductor device using the same.

The present inventors have made various studies to achieve the aboveobject and consequently achieved the present invention by finding that aheat dissipating material, which is obtained with a heat conductivefiller dispersed into a matrix, exerts excellent thermal conductivityand is not prone to oil bleeding when an addition-cured silicone gelwith a crosslink density adjusted and flexibility after curingcontrolled is used as the matrix, and a semiconductor device using thesame can be obtained.

An aspect of the present invention is a heat dissipating material,comprising: (A) 100 parts by weight of a silicone gel cured by anaddition reaction having a penetration (ASTM D1403, 1/4 cone) of notless than 100; and (B) 500 to 2000 parts by weight of a heat conductivefiller, wherein the heat dissipating material is interposed between aheat-generating electronic component and a heat dissipating body.

Another aspect of the present invention is a semiconductor device,comprising a heat-generating electronic component and a heat dissipatingbody with the heat dissipating material according to the aspect of thepresent invention interposed between the heat-generating electroniccomponent and the heat dissipating body.

The silicone gel according to the present invention means a curedmaterial of a low crosslink density partially having a three-dimensionalnetwork structure. It is clearly distinguished from a rubber-likeelastic material on the point that it has a rubber hardness value zeroaccording to JIS A Hardness, namely such low hardness not havingeffective rubber hardness, and a penetration of not less than 100according to ASTM D 1403 (¼ cone).

By configuring as described above, it is possible to provide a heatdissipating material excelling in thermal conductivity and not prone tooil bleeding and a semiconductor device using the same.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a sectional view showing an example of the semiconductordevice according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode of carrying out the present invention will be describedbelow. It is to be noted that the present invention is not limited tothe following embodiments.

The heat dissipating material according to an embodiment of the presentinvention comprises (A) a silicone gel cured by an addition reactionhaving a penetration (ASTM D1403, ¼ cone) of not less than 100 and (B) aheat conductive filler.

The component (A) the silicone gel cured by an addition reaction is usedas a matrix of a heat dissipating material, which is a componentproviding the heat dissipating material which is not prone to productionof oil bleeding. The component (A) is created by curing anaddition-curable silicone gel composition containing (A1)polyorganosiloxane having an average of 0.1 to 2 alkenyl groups, thealkenyl group being bonded to a silicon atom, within each molecule, (A2)polyorganohydrogensiloxane having two or more hydrogen atoms, thehydrogen atom being bonded to a silicon atom, within each molecule and(A3) a platinum based catalyst.

A component used as the component (A1) is represented by an averagecomposition formula:

R¹ _(a)R² _(b)SiO_([4−(a+b)]/2).

In the formula, R¹ represents an alkenyl group. The number of carbonatoms of the alkenyl group is preferably in a range of 2 to 8, andexamples thereof are a vinyl group, an allyl group, a propenyl group, a1-butenyl group, a 1-hexenyl group and the like, and more preferably avinyl group. The alkenyl group is contained in an average of 0.1 to 2,and preferably an average of 0.5 to 1.8 in each molecule. When thealkenyl group is less than an average of 0.1, polyorganosiloxanemolecules which do not contribute to the cross-linking reaction becometoo many, and it is hard to prepare a gel. Meanwhile, when they exceedan average of 2, (A) a silicone gel cured by an addition reaction(gel-like cured material) becomes too hard to obtain a desiredpenetration (a penetration of not less than 100 according to ASTM D1403, ¼ cone). And, the alkenyl group may be bonded to a silicon atom atthe terminal of the molecular chain, the silicon atom in the molecularchain, or both, but it is preferably bonded to at least the silicon atomat the terminal of the molecular chain, and particularly to the siliconatoms at both terminals of the molecular chain in view of the curingrate of the addition-curable silicone gel composition, the physicalproperties of the created (A) silicone gel cured by an addition reaction(gel-like cured material), and particularly flexibility.

R² is a substituted or unsubstituted monovalent hydrocarbon group nothaving an aliphatic unsaturated bond. R² has 1 to 12 carbon atoms, andpreferably 1 to 10 carbon atoms, and examples are an alkyl group such asa methyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, a hexyl group, an octyl group, a decyl group or a dodecylgroup; a cycloalkyl group such as a cyclopentyl group, a cyclohexylgroup or a cyclobutyl group; an aryl group such as a phenyl group, atolyl group, a xylyl group or a naphthyl group; an aralkyl group such asa benzyl group, a phenylethyl group or a phenylpropyl group; and a groupwhich has part or all of the hydrogen atoms substituted by a halogenatom such as a chlorine, fluorine or bromine atom, a cyanogen group orthe like, and examples are a halogenated hydrocarbon group such as achloromethyl group, a trifluoropropyl group, a chlorophenyl group, abromophenyl group, a dibromophenyl group, a tetrachlorophenyl group, afluorophenyl group or a difluorophenyl group, and a cyanoalkyl groupsuch as an α-cyanoethyl group, a β-cyanopropyl group or a γ-cyanopropylgroup. Among them, the alkyl group and the aryl group are preferable,and the methyl group and the phenyl group are more preferable.

Also in the formula, a and b are positive numbers satisfying 0<a<3,0<b<3 and 1<a+b<3. They are preferably 0.0005≦a≦1, 1.5≦b<2.4 and1.5<a+b<2.5, and more preferably 0.001≦a≦0.5, 1.8≦b≦2.1 and 1.8<a+b≦2.2.

The molecular structure of the component (A1) may be any of linear,branched, cyclic and three-dimensional networks (resin like) or amixture thereof.

The component (A1) preferably has a viscosity of 0.1 to 10 Pa·s at 23°C. When the viscosity is less than 0.1 Pa·s, the (A) silicone gel curedby an addition reaction (gel-like cured material) having good physicalproperties cannot be obtained and tends to become brittle. When itexceeds 10 Pa·s, workability tends to be degraded.

The component (A2) polyorganohydrogensiloxane is a cross-linking agentand has two or more hydrogen atoms (SiH group) that the hydrogen atom isbonded to the silicon atom within each molecule. The hydrogen atom maybe bonded to the silicon atom at the terminal of the molecular chain,the silicon atom in the molecular chain, or both. The molecularstructure may be any of linear, branched chain, cyclic andthree-dimensional networks, and may consist of them or a mixture of twoor more of them.

The component (A2) is represented by an average composition formula:

R³ _(c)H_(d)SiO_([4−(c+d)]/2).

In the formula, R³ represents a substituted or unsubstituted monovalenthydrocarbon group excepting an aliphatic unsaturated hydrocarbon group.Examples of R³ include an alkyl group such as a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, an isobutylgroup, a tert-butyl group, a hexyl group, a cyclohexyl group or an octylgroup; an aryl group such as a phenyl group or a tolyl group; an aralkylgroup such as a benzyl group or a phenylethyl group; and a group whichhas part or all of the hydrogen atoms in these groups substituted by ahalogen atom such as a chlorine, fluorine or bromine atom, or a cyanogroup, and examples are a chloromethyl group, a bromoethyl group, atrifluoropropyl group, and a cyanoethyl group. Among them, an alkylgroup having 1 to 4 carbon atoms is preferable, and a methyl group ismore preferable from and ease of synthesis and cost perspective.

In the formula, c and d are numerals satisfying 0.5≦c≦2, 0<d≦2 and0.5<c+d≦3, and preferably 0.6≦c≦1.9, 0.01≦d≦1.0 and 0.6≦c+d≦2.8.

The component (A2) preferably has a viscosity of 0.01 to 0.5 Pa·s at 23°C.

The blending amount of the component (A2) is an amount such that thetotal number of hydrogen atoms bonded to the silicon atoms becomes 0.3to 1.5, and preferably 0.4 to 1.2 to one alkenyl group bonded to thesilicon atoms of the component (A1). When it is less than 0.3, thedegree of cross-linking becomes insufficient, and it is hard to obtainthe (A) silicone gel cured by an addition reaction (gel-like curedmaterial). When it exceeds 1.5, it is hard to obtain the (A) siliconegel cured by an addition reaction (gel-like cured material) having adesired penetration (a penetration of not less than 100 according toASTM D 1403, ¼ cone), and furthermore, the physical properties tend tovary with time.

The component (A3) platinum based catalyst is a component foraccelerating the curing of the composition. As the component (A3), aknown catalyst used for hydrosilylation reaction can be used. Examplesinclude platinum black, platinum chloride, chloroplatinic acid, areactant of chloroplatinic acid and monohydric alcohol, a complex ofchloroplatinic acid and an olefin or vinylsiloxane, platinumbisacetoacetate and the like.

The blending amount of the component (A3) is an amount that is adequatefor curing and can be adjusted according to a desired curing rate or thelike. Generally, it preferably falls in a range of 1 to 100 ppm to thetotal amount of the addition-curable silicone gel composition inplatinum element equivalent.

The components (A1) to (A3) described above are determined as basiccomponents, and a reaction inhibitor may be added as an optionalcomponent in order to maintain appropriate curing reactivity and storagestability. Examples of the reaction inhibitor are acetylenic alcoholssuch as 3,5-dimethyl-1-hexyn-3-ol, 2-methyl-3-hexyn-2-ol and1-ethynyl-1-cyclohexanol, 3-methyl-3-pentene-1-yne,3,5-dimethyl-3-hexene-1-yne, or a methylvinylsiloxane cyclic compound,an organic nitrogen compound, an organic phosphorus compound and thelike. The blending amount of the reaction inhibitor is in a range suchthat the properties of the (A) silicone gel cured by an additionreaction (gel-like cured material) are not deteriorated, and preferably0.01 to 1 part by weight to 100 parts by weight of the component (A1).

For example, the component (A) silicone gel cured by an additionreaction, can be produced by mixing the above-described components (A1)to (A3) and the reaction inhibitor as an optional component by a mixersuch as a planetary mixer, a kneader or a Shinagawa mixer to obtain theaddition-curable silicone gel composition, and heating the mixture at 60to 150 degrees C. for 30 to 180 minutes to cure.

The penetration (ASTM D1403, ¼ cone) of the obtained component (A) isnot less than 100, preferably not less than 120, and more preferably 120to 220 to suppress oil bleeding at the time when the (B) heat conductivefiller is blended with the component (A) to use as a heat dissipatingmaterial and to obtain good physical conformity to the heat-generatingelectronic component and the heat dissipating body. The component (A)has flexibility at a degree that a viscosity cannot be substantiallymeasured by a rotational viscometer.

The component (B) is desired to be good in thermal conductivity, and itsexamples include inorganic powder such as aluminum oxide, zinc oxide,silicon oxide, silicon carbide, silicon nitride, magnesium oxide,aluminum nitride, boron nitride or graphite, and powder of metal such asaluminum, copper, silver, nickel, iron or stainless steel. One of themor a mixture of two or more of them may be used.

It has an average particle diameter of 0.1 to 100 μm, and preferably 0.1to 80 μm. When the average particle diameter is less than 0.1 μm, thedesired unworked penetration for a heat dissipating material (200 to 450at 23° C.) is difficult to obtain. Meanwhile, if the average particlediameter exceeds 100 μm, the heat dissipating material tends to havepoor stability. The average particle diameter can be determined by, forexample, a laser diffraction method. Its shape may be either sphericalor amorphous.

The blending amount of the component (B) is 500 to 2000 parts by weight,and preferably 600 to 1500 parts by weight to 100 parts by weight of thecomponent (A). If the blending amount is less than 500 parts by weight,the desired thermal conductivity of at least 1.0 W/(m·K) cannot beobtained. When it exceeds 2000 parts by weight, workability is degraded.

If necessary, to the above-described components (A) and (B) used as thebasic components, a flame retardancy providing agent, a heat resistanceimproving agent, a plasticizer, a coloring agent, an adhesion providingagent and the like may be added as optional components in an amount notimpairing the object of the present invention.

As a method of producing the heat dissipating material according to anembodiment of the present invention, there is, for example, a method ofmixing the components (A) and (B) and the optional components by a mixersuch as a planetary mixer, a kneader, a Shinagawa mixer or the like. The(B) heat conductive filler can be added to mix with the previouslyaddition-reacted (A) addition-curable silicone gel to prevent variationsin the heat dissipating characteristics due to the sedimentation of thecomponent (B). The obtained heat dissipating material has grease-likeproperties and extensibility. When it is coated, the surfaces of theheat-generating electronic component and the heat dissipating body arefirmly adhered without being affected by the irregularities of thesurfaces, and the interfacial thermal resistance can be reduced.

The unworked penetration of the heat dissipating material according tothe present invention is preferably 200 to 450. The unworked penetrationis indicated by a value according to JIS K 2220. When the unworkedpenetration exceeds 450 at 23° C., sagging tends to occur when coated.When it is less than 200, it is difficult to discharge and to havedesired thickness when coated on a heat-generating electronic componentby, for example, a syringe or a dispenser.

The heat dissipating material according to the present invention has athermal conductivity of 1.0 W/(m·K) or more, and preferably 1.5 W/(m·K)or more, at 23° C. when measured by a hot wire method. When the thermalconductivity is less than 1.0 W/(m·K), the heat conduction performancemight become insufficient, and usage tends to be limited.

The heat dissipating material according to the present invention exertsthermal conductivity and also excellent low bleeding property, so thatit is suitable as a heat conductive material to be interposed betweenthe heat-generating electronic component and the heat dissipating body.

The semiconductor device according to an embodiment of the presentinvention is described with reference to the drawing. FIG. 1 is asectional view showing an example of the semiconductor device accordingto the embodiment of the present invention.

As shown in FIG. 1, a semiconductor device 1 has a heat-generatingelectronic component such as a CPU 3 mounted on a wiring board 2 and aheat dissipating body such as a heat sink 4. The CPU 3 is covered with aheat spreader 5, and in this package is placed, for example, a knownheat conductive material such as a heat dissipating gel 6 between theheat spreader 5 and the CPU 3. Outside the package, a heat dissipatingmaterial 7, which is in a grease state, according to the above-describedembodiment of the present invention is interposed between the heatspreader 5 and the heat sink 4. Use of the heat dissipating material 7outside the package can provide excellent thermal conductivity and goodworkability.

The semiconductor device 1 is produced as follows. First, the heatdissipating gel 6 is coated on the CPU 3, which is mounted on the wiringboard 2, by a syringe or the like, and the package is assembled andheated. The heat dissipating material 7 which is in a grease state iscoated on the heat spreader 5 by a syringe or the like, and the heatsink 4 and the wiring board 2 are pressed by a clamp 8 or screws. Here,the heat dissipating material 7 is used outside (between the heatspreader 5 and the heat sink 4) of the package but not limited to suchan use and may also be used within (between the heat spreader 5 and theCPU 3) the package. When it is used within the package, contamination ofthe CPU 3 and the like can be prevented and reliability can be improvedbecause it has low bleeding properties.

It is preferable that the heat dissipating material 7 interposed betweenthe CPU 3 and the heat sink 4 has a thickness of 5 to 300 μm. When thethickness of the heat dissipating material 7 is less than 5 μm, there isa possibility of producing, for example, a gap between the heat spreader5 and the heat sink 4 because of slight deviations in pressure. When thethickness is greater than 300 μm, the heat resistance increases, and theheat dissipating effect tends to be degraded.

The present invention is described below with reference to examples, butthe present invention is not limited to the examples. In each ofExamples and Comparative Examples, a viscosity is indicated by a valueobtained by measuring at 23° C. And, an average particle diameterindicates a value measured by a laser diffraction method. The heatdissipating material obtained in Examples and Comparative Examples wereevaluated as follows and the results are shown in Table 1. Theproperties shown in Table 1 are indicated by values obtained bymeasuring at 23° C.

[Unworked Penetration]

It was measured according to JIS K 2220.

[Thermal Conductivity]

It was measured according to a hot wire method by a thermal conductivitymeter (QTM-500 produced by KYOTO ELECTRONICS MANUFACTURING CO., LTD.).

[Oil Bleeding Distance]

The obtained heat dissipating material was weighed for 0.1 g, which wasthen placed on a commercially available filter paper and put in an ovenat 105° C. The presence of oil bleeding around the heat dissipatingmaterial was measured for its length after one day, 10 days, 20 days and30 days.

Preparation Example 1

(A1) 100 parts by weight of polydimethylsiloxane having a viscosity of0.7 Pa's and an average of one vinyl group positioned at only theterminal of the molecular chain, (A2) 0.4 part by weight (SiH groupcontent of 8.8 mmol/g, SiH of (A2)/SiVi of (A1)=0.7) of a trimethylsilylgroup-blocked dimethylsiloxane/methylhydrogensiloxane copolymer having aviscosity of 0.015 Pa·s, (A3) 0.02 part by weight (4 ppm as platinumamount) of a vinylsiloxane complex compound (platinum amount: 1.8%) ofchloroplatinic acid, 0.02 part by weight of 3,5-dimethyl-1-hexyn-3-ol,and 0.2 part by weight of triarylisocyanurate were added to a universalkneader and mixed homogeneously. Further mixing was conducted at 150degrees C. for one hour to obtain (A-1) a silicone gel cured by anaddition reaction (an addition-cured silicone gel). The obtained (A-1)addition-cured silicone gel was found to have a penetration of 200 whenmeasured using a ¼ cone according to ASTM D1403. Its viscosity could notbe measured by a rotational viscometer (produced by SHIBAURA SYSTEMSCO., LTD.).

Preparation Example 2

(A1) 100 parts by weight of polydimethylsiloxane having a viscosity of0.7 Pa·s and an average of one vinyl group positioned at only theterminal of the molecular chain, (A2) 0.6 part by weight (SiH groupcontent of 8.8 mmol/g, SiH of (A2)/SiVi of (A1)=1.1) of a trimethylsilylgroup-blocked dimethylsiloxane/methylhydrogensiloxane copolymer having aviscosity of 0.015 Pa·s, (A3) 0.02 part by weight (4 ppm as platinumamount) of a vinylsiloxane complex compound (platinum amount: 1.8%) ofchloroplatinic acid, 0.02 part by weight of 3,5-dimethyl-1-hexyn-3-ol,and 0.2 part by weight of triarylisocyanurate were added to a universalkneader and mixed homogeneously. Further mixing was conducted at 150degrees C. for one hour to obtain (A-2) an addition-cured silicone gel.The obtained (A-2) addition-cured silicone gel was found to have apenetration of 120 when measured using a ¼ cone according to ASTM D1403.Its viscosity could not be measured by a rotational viscometer (producedby SHIBAURA SYSTEMS CO., LTD.).

Preparation Example 3

(A1) 100 parts by weight of polydimethylsiloxane having a viscosity of0.7 Pa·s and an average of one vinyl group positioned at only theterminal of the molecular chain, (A2) 0.7 part by weight (SiH groupcontent of 8.8 mmol/g, SiH of (A2)/SiVi of (A1)=1.2) of a trimethylsilylgroup-blocked dimethylsiloxane/methylhydrogensiloxane copolymer having aviscosity of 0.015 Pa·s, (A3) 0.02 part by weight (4 ppm as platinumamount) of a vinylsiloxane complex compound (platinum amount: 1.8%) ofchloroplatinic acid, 0.02 part by weight of 3,5-dimethyl-1-hexyn-3-oland 0.2 part by weight of triarylisocyanurate were added to a universalkneader and mixed homogeneously. Further mixing was conducted at 150degrees C. for one hour to obtain (A-3) an addition-cured silicone gel.The obtained (A-3) addition-cured silicone gel was found to have apenetration of 100 when measured using a ¼ cone according to ASTM D1403.Its viscosity could not be measured by a rotational viscometer (producedby SHIBAURA SYSTEMS CO., LTD.).

Preparation Example 4

(A1) 100 parts by weight of polydimethylsiloxane having a viscosity of0.7 Pa·s and an average of one vinyl group positioned at only theterminal of the molecular chain, (A2) 0.9 part by weight (SiH groupcontent of 8.8 mmol/g, SiH of (A2)/SiVi of (A1)=1.5) of a trimethylsilylgroup-blocked dimethylsiloxane/methylhydrogensiloxane copolymer having aviscosity of 0.015 Pa·s, (A3) 0.02 part by weight (4 ppm as platinumamount) of a vinylsiloxane complex compound (platinum amount 1.8%) ofchloroplatinic acid, 0.02 part by weight of 3,5-dimethyl-1-hexyn-3-oland 0.2 part by weight of triarylisocyanurate were added to a universalkneader and mixed homogeneously. Further mixing was conducted at 150degrees C. for one hour to obtain (A-4) an addition-cured silicone gel.The obtained (A-4) addition-cured silicone gel was found to have apenetration of 70 when measured using a ¼ cone according to ASTM D1403.Its viscosity could not be measured by a rotational viscometer (producedby SHIBAURA SYSTEMS CO., LTD.).

Example 1

(A-1) 100 parts by weight of the addition-cured silicone gel obtained inPreparation Example 1 was put into a one-liter universal kneader. And(B-1) 262 parts by weight of aluminum oxide powder having an averageparticle diameter of 14 μm, (B-2) 262 parts by weight of aluminum oxidepowder having an average particle diameter of 3 μm and (B-3) 131 partsby weight of zinc oxide powder having an average particle diameter of0.5 μm were also added. They were mixed homogeneously to obtain a heatdissipating material. The heat dissipating material was measured for itsproperties, and the results were shown in Table 1.

Example 2

(A-2) 100 parts by weight of the addition-cured silicone gel obtained inPreparation Example 2 was put into a one-liter universal kneader. And(B-1) 262 parts by weight of aluminum oxide powder having an averageparticle diameter of 14 μm, (B-2) 262 parts by weight of aluminum oxidepowder having an average particle diameter of 3 μm and (B-3) 131 partsby weight of zinc oxide powder having an average particle diameter of0.5 μm were also added. They were mixed homogeneously to obtain a heatdissipating material. The heat dissipating material was measured for itsproperties, and the results were shown in Table 1.

Example 3

(A-3) 100 parts by weight of the addition-cured silicone gel obtained inPreparation Example 3 was put into a one-liter universal kneader. And(B-1) 262 parts by weight of aluminum oxide powder having an averageparticle diameter of 14 μm, (B-2) 262 parts by weight of aluminum oxidepowder having an average particle diameter of 3 μm and (B-3) 131 partsby weight of zinc oxide powder having an average particle diameter of0.5 μm were also added. They were mixed homogeneously to obtain a heatdissipating material. The heat dissipating material was measured for itsproperties, and the results were shown in Table 1.

Comparative Example 1

(A-4) 100 parts by weight of the addition-cured silicone gel obtained inPreparation Example 4 was put into a one-liter universal kneader. And(B-1) 200 parts by weight of aluminum oxide powder having an averageparticle diameter of 14 μm, (B-2) 200 parts by weight of aluminum oxidepowder having an average particle diameter of 3 μm and (B-3) 130 partsby weight of zinc oxide powder having an average particle diameter of0.5 μm were also added. They were mixed homogeneously to obtain a heatdissipating material. The heat dissipating material was measured for itsproperties, and the results were shown in Table 1.

Comparative Example 2

(A-5) 100 parts by weight of C₁₀ modified silicone oil having aviscosity of 0.7 Pa·s (penetration: unmeasurable), (B-1) 320 parts byweight of aluminum oxide powder having an average particle diameter of14 μm, (B-2) 320 parts by weight of aluminum oxide powder having anaverage particle diameter of 3 μm and (B-3) 160 parts by weight of zincoxide powder having an average particle diameter of 0.5 μm were added toa one-liter universal kneader. They were mixed homogeneously to obtain aheat dissipating material. The heat dissipating material was measuredfor its properties, and the results were shown in Table 1.

Comparative Example 3

(A-5) 100 parts by weight of C₁₀ modified silicone oil having aviscosity of 0.7 Pa·s (penetration: unmeasurable), (B-1) 700 parts byweight of aluminum oxide powder having an average particle diameter of14 μm and (B-3) 400 parts by weight of zinc oxide powder having anaverage particle diameter of 0.5 μm were added to a one-liter universalkneader. They were mixed homogeneously to obtain a heat dissipatingmaterial. The heat dissipating material was measured for its properties,and the results were shown in Table 1.

TABLE 1 Example Example Example Comparative Comparative Comparative 1 23 Example 1 Example 2 Example 3 Component (A) A-1: Addition-curedsilicone gel 100 — — — — — (penetration of 200) A-2: Addition-curedsilicone gel — 100 — — — — (penetration of 120) A-3: Addition-curedsilicone gel — — 100 — — — (penetration of 100) A-4: Addition-curedsilicone gel 100 (penetration of 70) A-5: C₁₀ modified silicone oil — —— — 100 100 (0.7 Pa · s by rotational viscometer) Component (B) B-1:Aluminum oxide powder 262 262 262 200 320 700 (average particle diameterof 14 μm) B-2: Aluminum oxide powder 262 262 262 200 320 — (averageparticle diameter of 3 μm) B-3: Zinc oxide powder 131 131 131 130 160400 (average particle diameter of 0.5 μm) Unworked penetration 270 245210 180 400 250 Heat conductivity [W/m · k] 1.5 1.5 1.5 1.0 2.0 3.3 Oilbleed distance [mm] After one day 0 0 0 0 7 5 After 10 days 1 1 1 1 1510 After 20 days 3 3 1 1 20 12 After 30 days 3 4 2 1 24 14

It is apparent from Table 1 that the individual Examples using thesilicone gel cured by an addition reaction having a penetration of notless than 100 as the component (A) can obtain a heat dissipatingmaterial that exhibits very limited oil bleeding. Since high filling ofthe heat conductive filler is possible, excellent thermal conductivitycan be exerted.

INDUSTRIAL APPLICABILITY

The heat dissipating material of the present invention is excellent inthermal conductivity and not prone to oil bleeding, so it is suitable asa heat conductive material to be interposed between the heat-generatingelectronic component and the heat dissipating body.

1. A method of producing a heat dissipating material which is interposedbetween a heat-generating electronic component and a heat dissipatingbody, comprising: a step of mixing (A1) 100 parts by weight ofpolyorganosiloxane having an average of 0.1 to 2 alkenyl groups withineach molecule, the alkenyl group being bonded to a silicon atom, (A2) anamount of polyorganohydrogensiloxane having two or more hydrogen atomswithin each molecule, the hydrogen atom being bonded to a silicon atomthat the silicon-bonded hydrogen atom is 0.3 to 1.5 mole per one ofsilicon-bonded alkenyl group of the component (A1), and (A3) a catalyticamount of a platinum based catalyst to form an addition-curable siliconegel composition, a step of heating the addition-curable silicone gelcomposition at 60 to 150 degrees C. for 30 to 180 minutes to cure, astep of adding (B) 500 to 2000 parts by weight of a heat conductivefiller to (A) 100 parts by weight of the cured silicone gel and mixing.2. The method of producing a heat dissipating material according toclaim 1, wherein the cured silicone gel has a penetration (ASTM D1403, ¼cone) of not less than
 100. 3. The method of producing a heatdissipating material according to claim 1, wherein an unworkedpenetration at 23° C. of the heat dissipating material is in a range of200 to 450.